In recent years, due to the growing interest in energy saving, requests have been increasing for the near-infrared reflective film which shields transmission of heat ray of sunlight by equipping the windowpane of the buildings or the vehicles from a viewpoint of reducing the load according to air conditioning equipment.
Conventionally, dry film forming methods such as a vapor deposition method or a sputter method were proposed as the method of producing the near-infrared reflective film in which laminated films were formed by laminating the high refractive index layer and the low refractive index layer by turns. However, since the dry film forming methods need large-sized vacuum equipment, there are issues such that it requires high manufacture cost, and it is difficult to form large area film, and the support is limited to a heat resistant material due to being processed generally at high temperature.
With respect to the above issues, disclosed were methods for forming films by using wet coating methods such as a method of using ultraviolet curable resin (for example, refer to Patent Document 1) or a method for laminating TiO2 sol/SiO2 sol by turns (for example, refer to Patent Document 2).
However, in the film forming method using ultraviolet curable resin, since the low refractive index layer and the high refractive index layer are repeatedly coated, dried and cured by turns, productivity becomes poor and further due to a convection occurred in the coated layer at a time of drying, there are issues in which the uniformity in plane of each refractive index layers decreases and results in the refractive index unevenness. Similarly in the film forming method using sol, during a process where particles are aggregated to be bound, the uniformity of the refractive index in plane of each refractive index layers decreases and finally results in causing the refractive surface unevenness.